linux-kernel - [PATCH 13/20] x86/tdx: Rewrite hv_tdx_hypercall() without __tdx

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Date: Fri, 17 May 2024 17:19:31 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>,
	Dexuan Cui <decui@...rosoft.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Cc: linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	linux-hyperv@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH 13/20] x86/tdx: Rewrite hv_tdx_hypercall() without __tdx_hypercall()

Rewrite hv_tdx_hypercall() in assembly to remove one more
__tdx_hypercall() user.

tdvmcall_trampoline() cannot be used here as Hyper-V uses R8 and RDX to
pass down parameters which is incompatible with tdvmcall_trampoline()

The rewrite cuts code bloat substantially:

Function                                     old     new   delta
hv_tdx_hypercall                             171      42    -129

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 arch/x86/coco/tdx/tdcall.S | 30 ++++++++++++++++++++++++++++++
 arch/x86/hyperv/ivm.c      | 14 --------------
 2 files changed, 30 insertions(+), 14 deletions(-)

diff --git a/arch/x86/coco/tdx/tdcall.S b/arch/x86/coco/tdx/tdcall.S
index 269e5789672a..5b60b9c8799f 100644
--- a/arch/x86/coco/tdx/tdcall.S
+++ b/arch/x86/coco/tdx/tdcall.S
@@ -138,3 +138,33 @@ SYM_FUNC_START(tdvmcall_report_fatal_error)
 
 	ud2
 SYM_FUNC_END(tdvmcall_report_fatal_error)
+
+#ifdef CONFIG_HYPERV
+/*
+ * hv_tdx_hypercall() - Issue Hyper-V hypercall
+ *
+ * RDI - Hypercall ID
+ * RSI - Parameter 1
+ * RCX - Parameter 2
+ */
+SYM_FUNC_START(hv_tdx_hypercall)
+	movq	%rdi, %r10
+	movq    %rsi, %rdx
+	movq    %rcx, %r8
+
+	movq	$TDG_VP_VMCALL, %rax
+	movq    $(TDX_R8 | TDX_R10 | TDX_RDX), %rcx
+
+	tdcall
+
+	/* TDG.VP.VMCALL never fails on correct use. Panic if it fails. */
+	testq   %rax, %rax
+	jnz	.Lpanic_hv
+
+	movq	%r11, %rax
+
+	RET
+.Lpanic_hv:
+	ud2
+SYM_FUNC_END(hv_tdx_hypercall)
+#endif
diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index 18d0892d9fc4..562980e19d68 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -401,20 +401,6 @@ static void hv_tdx_msr_read(u64 msr, u64 *val)
 	if (WARN_ONCE(ret, "Failed to emulate MSR read: %lld\n", ret))
 		*val = 0;
 }
-
-u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2)
-{
-	struct tdx_module_args args = { };
-
-	args.r10 = control;
-	args.rdx = param1;
-	args.r8  = param2;
-
-	(void)__tdx_hypercall(&args);
-
-	return args.r11;
-}
-
 #else
 static inline void hv_tdx_msr_write(u64 msr, u64 value) {}
 static inline void hv_tdx_msr_read(u64 msr, u64 *value) {}
-- 
2.43.0